2015-01-17 14:53:18 -05:00
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.TH RDJPGCOM 1 "02 April 2009"
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.SH NAME
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rdjpgcom \- display text comments from a JPEG file
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.SH SYNOPSIS
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.B rdjpgcom
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[
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.B \-raw
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]
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[
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.B \-verbose
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]
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[
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.I filename
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]
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.LP
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.SH DESCRIPTION
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.LP
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.B rdjpgcom
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reads the named JPEG/JFIF file, or the standard input if no file is named,
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and prints any text comments found in the file on the standard output.
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.PP
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The JPEG standard allows "comment" (COM) blocks to occur within a JPEG file.
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Although the standard doesn't actually define what COM blocks are for, they
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are widely used to hold user-supplied text strings. This lets you add
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annotations, titles, index terms, etc to your JPEG files, and later retrieve
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them as text. COM blocks do not interfere with the image stored in the JPEG
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file. The maximum size of a COM block is 64K, but you can have as many of
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them as you like in one JPEG file.
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.SH OPTIONS
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.TP
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.B \-raw
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Normally
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.B rdjpgcom
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escapes non-printable characters in comments, for security reasons.
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This option avoids that.
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.PP
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.B \-verbose
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Causes
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.B rdjpgcom
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to also display the JPEG image dimensions.
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.PP
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Switch names may be abbreviated, and are not case sensitive.
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.SH HINTS
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.B rdjpgcom
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does not depend on the IJG JPEG library. Its source code is intended as an
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illustration of the minimum amount of code required to parse a JPEG file
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header correctly.
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.PP
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In
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.B \-verbose
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mode,
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.B rdjpgcom
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will also attempt to print the contents of any "APP12" markers as text.
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Some digital cameras produce APP12 markers containing useful textual
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information. If you like, you can modify the source code to print
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other APPn marker types as well.
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.SH SEE ALSO
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.BR cjpeg (1),
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.BR djpeg (1),
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.BR jpegtran (1),
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.BR wrjpgcom (1)
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.SH AUTHOR
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Independent JPEG Group
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